This invention complements another invention titled, “Methods for Making a Multicomponent Hemostatic Dressing,” disclosed in patent application PCT/IB2006/053526 filed on 27 Sep. 2006, which is incorporated by reference herein. That invention discloses a method of making a fibrous, pliable, bioabsorbable hemostatic dressing in which one of the process steps involves forming fibers from the homogeneous mixture, which essentially is the step that creates the fibrous base of the bandage, also referred to as the backing or scaffolding of the dressing. The present invention sets forth a new method of forming the fibers compatible with this earlier invention. In addition, the present invention can be used independently to manufacture a multi-component hemostatic bandage. As importantly, the present invention enables manufacture of a bandage with a high surface area per unit weight of exposed active ingredients to rapidly effect blood clotting in a wound.
Hemostatic compositions of the present invention are also generally referred to as bandages or wound dressings. During the three decades preceding this invention, an understanding of the human immunodeficiency virus (HIV) and hepatitis propagation risks stemming from use of unpurified blood and blood derivatives hindered the safe development of human fibrinogen-based hemostatic bandages. However, later improvements on recombinant fibrinogen and recombinant blood factors technologies, as well as on plasma purification techniques, reopened opportunities for hemostatic bandage development.
Fibers for bandages are typically made by methods, such as melt blowing, extrusion, other fiber drawing techniques, and electrostatic spinning, or simply electrospinning. In this last method, a polymer is dissolved in a solvent or melted and placed in a glass pipette tube as a precursor liquid, that is, a fiber-forming liquid composition used to make the fibers. A tapered orifice or nozzle at one end of the tube is used to spin out or spray out a liquid stream that forms a fiber. A high voltage potential up to 50 kilovolts is applied between the polymer solution and a collector near the nozzle. This process can produce nanofibers with diameters as low as 50 nanometers, although the collected web usually contains fibers with varying diameters from 30 nanometers to over one micron. The production rate of this process is slow and often measured in quantities that are less than one gram per hour per nozzle, and the fiber strength is usually low, creating a fragile fiber.
Methods of electrospinning fibers for dressings that contain coagulation proteins are also well known. For example, United States Patent Application Publication No. 20060013863 A1 to S. W. Shalaby, et al., describes such methods and the formation of hemostatic, compliant, elastomeric, multicomponent, fibrous dressings. This prior art, however, does not teach a micrometer or sub-micrometer scale coating of the fibers. Rather, Shalaby teaches achieving bicomponent fibers through controlling the polymer molecular weight; the type of spinning solvent and hence, the solvent-polymer interaction; the concentration of the individual polymers; and the electrospinning parameters. These fiber fabrication techniques are different from the present invention and the core and sheath fiber produced do not have dispersion of the active at or near molecular level, so that there are no core-sheath distinctive regions in the fibers produced according to the present invention.
Despite this prior art, electrospinning of aqueous protein solutions is generally problematic because the chemical solution compromises the chemical stability or shelf-life of the proteins. One approach to overcome this shortcoming is spinning the bandage right on the wound at the time it is needed. PCT application WO/1998/003267 by R. A. Coffee, is an example. Electrospinning a bandage directly on a wound had an initial appeal of making the fibers directly off blood coagulation proteins, avoiding a fibrous backing and minimizing protein stability or shelf-life problems in pre-made bandages. However, practical problems in using this approach in situations involving arterial bleeding are that it is time consuming and requires a level of skill not often present in environments such as the battlefield. For direct application by electrospinning of aqueous protein solutions to wounds, two additional problems became evident: this electrospinning approach uses a lot more protein than by just coating biocompatible polymer fibers, such as those made from polylactic acid; and, electrospinning of proteins in fluorinated hydrocarbons is cell-toxic if even a trace fluorinated hydrocarbon remains in the fibers. The present invention does not make a dressing or bandage at the time it is needed at the emergency situation. Rather it is suited only for making the dressing in a manufacturing facility, packaging it, and shipping it for later use.
The method of the present invention uses a rotating disk and does not use a nozzle to create fibers of a bandage. These fibers may form the entire bandage or may be used as the scaffolding or fibrous backing in other bandage processing steps. Dressings produced according to the invention are characterized by the proximity of the different procoagulation constituents that would otherwise react prematurely on molecular contact. The fibers created by the method are pliable and much stronger than otherwise achievable for effective dressings. Another important characteristic of the present invention is a substantially higher manufacturing rate for fibers than conventional flow-through-orifice electrospinning and electrospray methods.
The present invention offers the capability of incorporating, on molecular-, micrometer- and sub-micrometer-scales, pro-coagulation species, either natural or synthetic, into the fiber-forming liquid composition used to make the fibers, and this is a desirable improvement. In addition, fibrinogen and/or other blood clotting species are incorporated in a micrometer or sub-micrometer scale coating on the fibers of the dressing. Fiber coatings of this scale typically means a coating thickness from about five to one hundredth of a micrometer.
In the present invention, fiber forming liquid is introduced at or near the center of a rotating disk such that fibers are spun off the rim of the disk. Use of a rotary device ensures adequate bandage production rates. Perhaps as importantly, the rotary device equipped with multiple feed lines, permits rapid customization of the fibers in a backing using one apparatus, simply by turning off one feed line and turning on another. This is important in that it allows for rapidly changing the fiber composition for a single bandage, for example in a sequential fashion, to include pro-coagulation species in a first set of fibers that would otherwise chemically react or conflict with the pro-coagulation species in a second set of fibers if used together.
A significant component of prior art that includes fibrinogen or other blood clotting species in a dressing are not fiber coatings, but are typically in multiple layers on the overall bandage, which is, generally, evident to the naked eye. A micrometer or sub-micrometer scale coating on the fibers is a more thorough distribution of the blood clotting species and cannot be discerned with the naked eye. In the prior art, the surface of each such distinct bandage layer exposes the blood clotting species to blood and surrounding air. Each such distinct layer has a characteristic dimension, such as thickness and grain size, that is larger than the average fiber diameter and the thickness of the coating of blood clotting species on any fibers in the present invention.
In a departure from the distinct bandage layer technology, U.S. Pat. No. 6,056,970 to K. E. Greenawalt, et al. teaches a fibrous dressing wherein the coagulation protein is dispersed throughout the hemostatic composition, but not in a molecular-scale coating on the bulk of the fibers in the dressing. Rather Greenawalt discloses dispersal within the fibers in a manner that captures comparatively larger domains of the protein within the fiber structure. Greenawalt also teaches compressing the fibers into paper-like compositions so as to prevent activation of fibrinogen during processing. The present invention is an improvement in that the protein is captured both within a fiber and as a micrometer or sub-micrometer scale coating on the fibers, such that it significantly increases the surface area of exposure of coagulation protein to the blood.
The method of the present invention offers significant manufacturing efficiencies in using a single apparatus to make a fibrous bandage with coated fibers. Avoiding processing steps that employ different equipment, provides efficiency and speed not available in the current state of the art.
The method of the present invention offers manufacturing flexibility in that different coating steps for the blood clotting species may be easily accomplished with the same apparatus. Essentially, what is required are separate feed lines for introducing the differing blood clotting species at the center of the rotating disk. In addition to flexibility, separate feed lines and separate coatings enable placement of the blood coagulation proteins in very close proximity to each other, even when such proteins cannot coexist together in solution or in intimate molecular contact. For example, fibrinogen and thrombin can be used in separate coatings without significant reaction into fibrin.
These capabilities translate to a substantially higher throughput than conventional flow-through-orifice electrospinning and electrospray methods. Both fiber backing and blood clotting species may be made and sequentially applied to a single bandage using the same apparatus, and flexibility in tailoring bandages for particular applications is enhanced by enabling choices in the order by which fiber and blood clotting species coating steps are introduced on the bandage.
As an example of such sequential application in a single bandage, the present invention enables formation of biopolymer fibers containing fibrinogen, and once dry, formation of biopolymer fibers containing of thrombin. This bandage, thus, has two dry layers of fiber containing different procoagulant species. The bandage is created using a single and modular bandage manufacturing unit operating continuously. The fibers made in each run can be made as thin as several micrometers each. Another example is biopolymer fibers made first then coated with fibrinogen, coated again with biopolymer to serve as a separation coating, then coated with thrombin.
Three key elements represent improvement over prior art dealing with fibrous thrombin-fibrinogen bandage structures. First, dispersion of the protein coatings in the micrometer and sub-micrometer range guarantee a high surface area per unit weight exposed to gushing blood coming off an arterial wound, which is essential for clot formation in the order of seconds. Second, proteins such as thrombin and fibrinogen that would otherwise initiate blood coagulation cascade reactions on molecular contact, thereby significantly reducing the shelf-life of the hemostatic bandage, are kept in separate coatings but, more importantly, at distances ranging from one micron to one millimeter to ensure very rapid interaction between these two coagulation cascade proteins on contact with blood from a wound. Third, the ultrafine biocompatible fiber backing is meant to provide a strong scaffolding effect during formation of a blood clot at the arterial wound site.
There are a number of synthetic agents that can potentially improve the performance of fibrinogen-based hemostatic bandages, besides natural ones such as thrombin, prethrombin, Factor XIIIa and other blood coagulation factors. Very recently, the use of propyl gallate and other gallate derivatives has been disclosed to increase the performance of fibrinogen-based hemostatic dressings with hemostatic dressing backings made, among other things, of collagen. U.S. Pat. No. 6,891,077 to S. W. Rothwell, et al., is an example disclosing this use. Propyl gallate is also used in the food industry as an antioxidant additive for oils and fats. The present invention newly creates the option of occluding propyl gallate and its derivatives within the fibers of the dressing. The Rothwell patent teaches a method of adding a solution of propyl gallate to a bandage, but does not teach using propyl gallate dispersed into the bulk of fibers.
The United States Army has recently used a fibrinogen bandage with a chitosan backing in the battlefield. Besides chitosan, which is a biopolymer derived from the chitin in crustaceans, other polymers such as but not limited to polylactic acid and polylactic-co-glycolic acid and combinations thereof, may be viewed as good fiber precursors for a fibrinogen-containing wound dressing. Polylactic acid and polylactic-co-glycolic acid degrade in vivo by hydrolysis (esterase activity) into lactic acid and glycolic acid, respectively, which are then incorporated into the tricarboxylic acid metabolic cycle. Besides polylactic acid and polylactic-co-glycolic acid, other bioabsorbable polymers such as, but not limited to, polycaprolactone, and copolymers resulting from combinations thereof, may be used as fiber precursors for hemostatic dressings and the present invention permits full utilization of these materials thoroughly mixed in the fibers of the bandage.
Fibrinogen has been recently processed into fibers by electrospinning from 1,1,1,3,3,3-hexafluoroisopropanol solutions. Besides being soluble in water, proteins are often soluble in perfluorinated alcohols such as 1,1,1,3,3,3-hexafluoroisopropanol, and 2,2,2-trifluoropropanol. The acute toxicity of 1,1,1,3,3,3-hexafluoroisopropanol, however, is well documented. Despite the acute toxicity problems, a number of patent applications still describe methods for direct electrospinning of protein solutions in organic solvents for making hemostatic and wound dressings. For example, two of these include United States Patent Application Publication Nos. 20040037813 for electrospun collagen and 20040229333 for electroprocessed fibrin.
The pouring of a fluid at or near the center of a rotating disk in the presence of electric fields as a means for liquid atomization is well known. Besides their traditional use for spraying paint, Balachandran and Bailey for example (W. Balachandran and A. G. Bailey, ‘The Dispersion of Liquids Using Centrifugal and Electrostatic Forces’, IEEE Transactions on Industry Applications, Vol. 1A-20, No. 3, 682-686 (1984)) described the modes by which hydrocarbon oils of varying resistivity values are accelerated from the edge of the rotating disk toward an annular counterelectrode.
This prior art does not teach the manufacture of a bandage nor does it describe the elements needed to create a functional hemostatic bandage composed of coated fibers or multicomponent fibers assembled into a dressing. The present invention applies a rotating disk apparatus under a innovative set of control conditions to manufacture a fibrous hemostatic bandage with attributes missing from, and needed to improve, the art of manufacturing hemostatic dressing.